Gmail briefly stopped working, leaving huge numbers of people unable to read their emails.
The website and app appeared to be down and failed to load.
Users reported seeing a strange "error 404" instead of their messages.
"404. That's an error," the message read, alongside a picture of a broken robot. "The requested URL was not found on this server. That's all we know."
Problems were hitting users all over the world, according to the site Down Detector. While they were particularly focused in western Europe, that is likely to be a result of timezones meaning most users are online there.
Google said the problem had now been fixed.
"The problem with Gmail should be resolved," it posted on its support page. "We apologize for the inconvenience and thank you for your patience and continued support.
"Please rest assured that system reliability is a top priority at Google, and we are making continuous improvements to make our systems better."
Google had said earlier that it was aware of the problem and would be posting updates as it attempted to fix it.
"We're aware of a problem with Gmail affecting a significant subset of users," the Gmail status page read. "The affected users are unable to access Gmail.
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